The present application relates to the following U.S. Patent Applications, all filed concurrently herewith on Sep. 24, 2001, and all of which are expressly incorporated herein by reference in their entireties: xe2x80x9cZOOM LENS MECHANISMxe2x80x9d having attorney U.S. patent application Ser. No. 09/960,309, xe2x80x9cLENS DRIVE MECHANISMxe2x80x9d having application Ser. No. 09/960,382, xe2x80x9cECCENTRICITY-PREVENTION MECHANISM FOR A PAIR OF LENS-SUPPORTING RINGSxe2x80x9d having application Ser. No. 09/960.515, xe2x80x9cREDUCTION GEAR MECHANISMxe2x80x9d having application Ser. No. 09/960.52 1, xe2x80x9cRING MEMBER SHIFT MECHANISM AND LENS GROUP SHIFT MECHANISMxe2x80x9d having application Ser. No. 09/960,518, xe2x80x9cLENS BARRELxe2x80x9d having application Ser. No. 09/961,231, xe2x80x9cLENS BARRELxe2x80x9d having application Ser. No. 09/960,516, xe2x80x9cLENS BARRELxe2x80x9d having application Ser. No. 09/961,233, xe2x80x9cZOOM LENS BARRELxe2x80x9d having application Ser. No. 09/961,185, and xe2x80x9cLENS BARRELxe2x80x9d having application Ser. No. 09/961,232, each naming as inventors Hiroshi NOMURA et al.; and xe2x80x9cLENS DRIVE CONTROL APPARATUS FOR ZOOM LENS SYSTEM HAVING A SWITCHING LENS GROUPxe2x80x9d having application Ser. No. 09/961,186 and naming as inventor Norio NUMAKO.
1. Field of the Invention
The present invention relates to lens drive mechanisms, and more particularly, to lens drive mechanisms for alternatively moving two sub-lens groups toward and away from each other or moving the two sub-lens groups integrally.
2. Description of the Related Art
In a zoom lens system of the prior art, there are contradictory demands for a high zoom ratio and miniaturization. For example, in a two-lens-group zoom lens system which can be miniaturized, if the paths of the lens groups thereof (hereinafter, zoom paths) are determined (i.e., solutions for zoom paths) so that the zoom ratio becomes high, interference of the lens groups occurs on the telephoto side, or interference of a lens group and the image plane occurs on the wide-angle side. On the other hand, in a three-lens-group zoom lens system, the zoom ratio thereof can be made higher than that of a two-lens-group zoom lens system; however, miniaturization is difficult. Furthermore, if an attempt is made to obtain a higher zoom ratio, and if the power of these three lens groups is determined accordingly, precision on the operations of the zoom lens system cannot be obtained due to the mechanical structure thereof.
The assignee of the present application has proposed an unprecedented zoom lens system that meets the contradictory demands of high zoom ratio and miniaturization (U.S. patent application Ser. No. 09/534,307, Japanese Patent Application No. Hei 11-79572). This zoom lens system has the following characteristics: it includes a plurality of movable lens groups for varying the focal length; at least one of the lens groups is a switching lens group which includes two sub-lens groups, one of the sub-lens groups being a movable sub-lens group that can be selectively positioned at either one movement extremities in the optical axis direction with respect to the other sub-lens group; the movable sub-lens group of the switching lens group is positioned at an extremity of a short-focal-length zooming range, from the short focal length extremity to an intermediate focal length, and at the opposite extremity of a long-focal-length zooming range, from the intermediate focal length to a long focal length extremity; and zoom paths of the switching lens group and the other lens groups are discontinuous at the intermediate focal length and are defined to focus on a predetermined image plane corresponding to the position of the movable sub-lens group. There may be one or more intermediate focal lengths.
In such a zoom lens system, while the two sub-lens groups (i.e., the switching lens group) are moved to a mutually close position and mutually distant position during the switching between the short-focal-length side zooming range and the long-focal-length side zooming range, the two sub-lens groups can also be moved integrally regardless of zooming range to carry out focusing. In the case where the two sub-lens groups are alternatively moved toward and away from each other (i.e., to the mutually close position or mutually distant position) or moved integrally, if the sub-lens group frames, each of which supports one of the sub-lens groups, are individually guided, guide mechanisms for guiding the sub-lens group frames may interfere with each other when the sub-lens group frames are moved integrally. As a result, smooth guiding may be interrupted.
Accordingly, it is an object of the present invention to provide a simple lens drive mechanism that ensures smooth movements of two sub-lens groups toward and away from each other as well as smooth integral movements of the two sub-lens groups without causing interference between guiding elements.
In order to achieve the above object, a lens drive mechanism is provided, including a first sub-lens group frame and a second sub-lens group frame for supporting a first sub-lens group and a second sub-lens group, respectively, the sub-lens groups functioning optically in a mutually close position and in a mutually distant position, with respect to the optical axis thereof; a support frame for supporting the first sub-lens group frame and the second sub-lens group frame; a first linear guide mechanism provided between the first sub-lens group frame and the support frame, the first linear guide mechanism guiding the first sub-lens group frame while permitting movement thereof in the optical axis direction and preventing rotation thereof about the optical axis; a second linear guide mechanism provided between the second sub-lens group frame and the support frame, the second linear guide mechanism guiding the second sub-lens group frame while limiting rotation of the second sub-lens group frame at two extremities of rotation thereof over a predetermined angle, and linearly guiding the second sub-lens group frame in the optical axis direction at the two extremities of rotation; a lens frame shift mechanism for causing the first sub-lens group frame and the second sub-lens group frame to move to the mutually close position and the mutually distant position, in accordance with rotation of the second sub-lens group frame between the two extremities of rotation; and a linear displacement mechanism which integrally moves the first sub-lens group frame and the second sub-lens group frame in the optical axis direction, in the mutually close position and in the mutually distant position. A linear guide clearance of the first linear guide mechanism is larger than a linear guide clearance of the second linear guide mechanism.
In an embodiment, the first and second sub-lens groups form one of a plurality of variable lens groups for varying a focal length thereof, and the first and second sub-lens groups constitute a focusing lens group which advances or retreats in the optical axis direction while maintaining the mutually close position or at the mutually distant position, regardless of the focal length.
Preferably, the lens frame shift mechanism includes a cam surface and a follower provided on opposed surfaces of the first sub-lens group frame and the second sub-lens group frame, the cam surface and the follower being arranged so as to move the first sub-lens group frame and the second sub-lens group frame to the mutually close position and the mutually distant position as the second sub-lens group frame is rotated.
Preferably, the lens drive mechanism further includes a positioning recess formed as a continuation of the opposite ends of the cam surface, the positioning recess defining relative positions of the first sub-lens group frame and the second sub-lens group frame in the optical axis direction and in the circumferential direction by engaging with the follower when the first sub-lens group frame and the second sub-lens group frame are in the mutually close position and in the mutually distant position; and a biasing member for biasing the first and second sub-lens group frames to bring the positioning recess and the follower into engagement. The first sub-lens group frame and the second sub-lens group frame are held together in the mutually close position and in the mutually distant position due to the engagement of the follower and the positioning recess.
Preferably, the first linear guide mechanism includes a plurality of guide bores formed on the first sub-lens group frame at different positions in the circumferential direction, and a plurality of guide rods loosely fitted in each of the guide bores and secured to the support frame. Preferably, the second linear guide mechanism includes a plurality of guide projections formed on the second sub-lens group frame at different positions in the circumferential direction, and a close-position linear guide slot for the mutually close position and a distant-position linear guide slot for the mutually distant position, the close-position linear guide slot and distant-position linear guide slot being formed on an inner surface of the support frame at different positions in the circumferential direction to slidably receive each corresponding the plurality of guide projections.
Preferably, a rotation-permitting recess is further formed on the inner surface of the support frame in the circumferential direction, for allowing the guide projections to move between the close-position linear guide slot and the distant-position linear guide slot.
Preferably, an actuator ring is rotatably provided in the support frame and is rotated to cause the lens frame shift mechanism and the linear displacement mechanism to operate.
Preferably, the linear displacement mechanism includes a cam surface and a follower provided on opposed surfaces of the actuator ring and the second sub-lens group frame, the cam surface and the follower being arranged to move the second sub-lens group frame in the optical axis direction in accordance with rotation of the actuator ring when the second sub-lens group frame is guided by the second linear guide mechanism.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 2000-289385 (filed on Sep. 22, 2000) which is expressly incorporated herein in its entirety.